I have a 400 (core engine) in a '70 Challenger with headers and PS. Plug change requires some adaptation... but not too bad after figured out. Key tools are a short "wobble socket extension", short regular extension and a box wrench that fits the hex on my spark plug socket. On several holes, I fit the socket to plug and use the box wrench to tighten or loosen.

Hardest for me is getting the tight ones started back in. Often by feel with a short socket extension in my fingers.